Motor-control system



c. c. RUNNER.

MOTOR CONTROL SYSTEM.

APPLICATION FILED MAR. 14, 1918.

Patented July 27, 1920.

Inventor C laude C .Runne UNITED STATES PATENT ICE.

CLAUDE O. RUNNER, OF SCHENEC'IADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MOTOR-CONTROL SYSTEM.

Specification of Letters fatent.

Patented July 27, 1920.

Application filed March 14, 1918. Serial No. 222,413.

To all whom it may concern:

Be it known that I, CLAUDE C. RUNNER, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Motor-Control Systems, of .which the following is a specimanner.

My invention relates more specifically to motor control systems employing series electromagnetic switches or contactors for outting out the starting resistance. These series contactors which are energized in series with the armature and close upon a falling cur-- rent are now very commonly used for motor acceleration. While these contactors are designed to close at a very low current, it may sometimes happen that the armature/current is so small, due to a very light load or to the fact that the motor is running at or near fullspeed, that the contactor will not close. Furthermore, the construction of these contactors is usually such that an interlocking or auxiliary contact for weakening the field of the motor upon the closure of the contactor cannot be effectively employed. Moreover, from the very nature of the contactor it is evident that it will open when the armature current drops 'to a very low value or upon a current reversal due to a pump back?! In carrying out my invention, I overcome these difficulties and provide an arrangement in which the starting resistance will be cut out regardless of the low armature current; the field may be weakened without auxiliary contacts on the series contactor and the series contactor will be held closed independently of the armature current.

In the accompanying drawing in whichI have illustrated one form of my invention diagrammatically, L and B represent two electromagnetic switches which are mechanically interlocked, as shown, so that they cannot both be closed at the same time. Contactor L is a line switch for closing the main circuit and the contactor B is for closing a dynamic brake circuit through the brake resistance BR. A represents the armature 0f the motor to be controlled. F the commutating field and F the shunt field. 10 represents a series contactor for cutting out the starting resistance R and 11 represents a field rheostat for varying the strength of the shunt field F. The contactor L is energized through a normally open push button 12, there being an interlock 13 on the contactor for making the maintaining circuit independent of the starting button and also'a stop button 14 for deenergizing the contactor. The brake contactor B is normally open and is closed by the C. E. M. F. of the motor when the line contactor L is opened.

In addition to the above described apparatus which is commonly used for starting a motor, I employ a shunt contactor 18, the Winding of which is connected across the motor armature so as to be responsive to the counter elcctromotive force of the motor. The contacts of the switch of this contactor are in parallel with those of the series contactor 10, so that the resistance R will be cut out of circuit by the closure of either the series or the shunt contactor. This contactor 18 is arranged to operate a switch 16 which is normally closed to give maximum field strength. When the contactor closes, however, the switch 16 is opened, thereby inserting resistance from the field rheostat 11 in series with the shunt field winding. The circuit of the Winding of shunt contactor 18 is controlled by the brake contactor through an interlock 17 so that when the brake contactor is closed the shunt contactor cannot be energized;

As thus constructed and arranged the operation of my improved system is as follows: With the parts in the position shown in the drawing, the motor is started by pressing the push button 12 which energizes the line contactor L and makes a maintaining circuit through the stop push button 14:. The armature circuit is now completed from the positive side of the line through the contacts of the line contactor, through the armature A commutating field winding F, resistance and winding of series contactor 10 to the opposite side of the line. The, motor will now start with the resistance in series and as the motor speeds up the series contactor will close in a well understood manner and cut out the starting resistance R. It will be observed that the contactor 18 at starting is connected across the armature and is, therefore, responsive to the counter electromotive force of the motor. Uponthe closing of the series contactor 10, however, the shunt contactor 18 is connected across the line, the circuit being from the positive side of the line through interlocking contactor l7, thence through the contacts of the series contactor and the low resistance winding of the series contactor to the opposite side of the line. The shunt contactor will, therefore, close upon the closing of the series contactor. The closing of the shunt contactor opens the switch. 16 so as to insert a por tion of the resistance from the rheostat 11, depending upon the position of the rheostat arm, in circuit with the shunt field winding to increase the speed of the motor. The closing of the contactor 18 not only short circuits the resistance R but also the winding of the series contactor 10 so that the latter. will open. The starting resistance is now short circuited by the shunt contactor 18 and hence will not be affected by a drop in the armature current. Suppose now that the load on the motor isvery light so that upon closing the line contactor the current would not be sufficient to close the series contactor. In this case, in the absence of the contactor 18, the motor would run on the resistance, but by reason of the fact that this contactor is connected across the armature, it will close when the speed rises to a proper value. This speed will ordinarily be just above that corresponding to the normal full load current of the motor so that it will never close before the series contactor, but will close in case the series contactor fails to close. The motor will now run at full speed corresponding to the Weakened field conditions. To stop the motor the push button 14: is pressed, thereby opening the line contactor L to permit the brake contactor B to close, thereby establishing a dynamic braking circuit through the brake resistance BR and bringing the motor completely to rest. When the brake contactor closes, the shunt contactor 18 opens, thereby restoring the shunt field to full strength.

While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, as various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. A control system for electric motors comprising a starting resistance, an electromagnetic switch energized by the motor current to cut out the resistance when the motor current drops to a predetermined value and means controlled by the speed of the motor and independent of the motor current for cutting out the resistance whenthe motor current is below a value at which the electromagnetic switch will close.

2. A control system for electric motors comprising a starting resistance, an electromagnetic switch energized by the motor current to cut out the resistance when the motor current drops to a predetermined value and a switch controlled by the speed of the motor and independent of the armature current having its contacts in parallel with those of the electromagnetic switch.

3. A control system for electric motors comprising a starting resistance, an electromagnetic switch energized in series with the motor armature to cut out the resistance when the motor current drops to a predetermined 'value and an electromagnetic switch responsive to the counter-electr0mot-ive force of the motor and having its contacts in parallel with those of the series switch, said switch being connected to close upon the closure of the series switch.

4:. Acontrol system for electric motors comprising a starting resistance, an electromagnetic switch energized in series with the motor armature to cut out the resistance when the motor current drops to a predetermined value and an electromagnetic switch responsive to the counter-electromotive force of the motor and connected to close upon the closure of the series switch for weakening the field of the motor.

5. A control system for electric motors comprising a starting resistance, an electromagnetic switch energized in series with the motor armature to cut out the resistance when the motor current drops to a predetermined value and an electromagnetic switch having a shunt winding connected across the motor armature, main contacts in parallel with those of the series switch and auxiliary contacts for weakening the field of the motor, and connections whereby the shunt switch is energized to close in case either the speed of the motor increases to a predetermined value or the series switch first closes.

In witness whereof, I have hereunto set my hand this 13th day of March, 1918.

CLAUDE C. RUNNER. 

